This invention relates to a system for detecting and analyzing surfaces of samples.
With the advent of instruments such as the scanning tunneling microscope (STM), it is now possible to investigate the structure, spectra and dynamics of biological molecules and membranes as well as other substances at the atomic or molecular level. While more than a thousand STM's have been in operation and the instrument has sparked great interest in spectroscopy, the actual headway that has been made in this area remains rather modest. Thus, Bob Wilson and co-workers at IBM Almaden have made some progress in distinguishing closely related adsorbed surface species in STM images. G. Meijer et al., Nature 348, 621 (1990). In "Non-Linear Alternating-Current Tunneling Microscopy," Kochanski, Physical Review Letters, 62(19):2285-2288, May 1989, a method for scanning tunneling microscopy is described, where a non-linear alternating current (AC) technique is used that allows stable control of a microscope tip above insulating surfaces where direct current (DC) tunneling is not possible.
The STM has a counter electrode on which the sample to be investigated is placed and another electrode in the shape of a microscope probe with a tip placed at a small distance away from the sample surface. A DC or a low frequency AC signal is then applied across the pair of electrodes. The probe tip is then moved across the sample surface in a scanning operation and the changes in the current or voltage across the electrodes are monitored to detect the characteristics of the sample.
A number of specific implementations of the scanning tunneling microscope have been proposed. See, for example, "A Versatile Microwave-Frequency-Compatible Scanning Tunneling Microscope," by Stranick and Weiss, Rev. Sci. Instrum., 64(5):1232-1234, May 1993; "Coarse Tip Distance Adjustment and Positioner for a Scanning Tunneling Microscope," by Frohn et al., Rev. Sci. Instrum., 60(6):1200-1201, June 1989; a product brochure from Besocke Delta Phi GmbH of Juelich, Germany, entitled "The Beetle STM--A Versatile, UHV Compatible Scanning Tunneling Microscope," and "An Easily Operable Scanning Tunneling Microscope," by Besocke, Surface Science, 181:145-153, 1987. However, none of the above implementations has the capability of changing samples or microscope within the vacuum chamber.
Frequently, it is desirable to first prepare and/or characterize the sample in a vacuum chamber using instruments for ion sputtering or electron or mass spectroscopy, and then transfer the prepared/characterized sample to an STM for surface study. Since the implementations in the above-referenced articles and brochure are apparently not capable of transferring samples within the vacuum chamber, it would be difficult or impossible to accomplish the above-described process using such implementations. There is also a need to be able to transfer samples or change instruments in vacuum involving surface analytical instruments other than the STM. It is therefore desirable to provide an improved system for implementing surface detection and to handle different equipment required for preparation, detection and analysis of sample surfaces where it is possible to transfer samples and change instruments.